Dewaxing of oil



Patented Apr. 6, 1937 PATENT OFFICE DEWAXING OF 'OIL Leo D. Jones, Philadelphia, Pa auignor to The Sharples Specialty Company, Philadelphia, Pa a corporation of Delaware No Drawing. Application June 25, 1981, Serial N0. 548,922

17 Claims.

This invention relates to a process for producing lubricating oil having a low cold test and substantially free of a tendency to cloud, and to the product thereof.

The centrifugal dewaxing of wax-containing mineral oils for the production of lubricating oils having reduced cold test is now widely carried out commercially in accordance with Sharples Patents Nos. 1,232,104; 1,351,265; 1,416,890 and Oils which are successfully dewaxed commercially in accordance with the processes described in those patents include such fractions (that term being used herein to include in each instance both residues and distillates) as steamreflned cylinder stock residues having a flash point in the neighborhood of 525 F., long residues of petroleum produced by non-cracking distillation and having a flash point in the neighborhood of 450 F. or higher, and distillates produced by non-cracking distillation and having flash point in the neighborhood of 450 F. and higher flash points, and leaving residues varying from a flash point of 525 F. up to flux or brittle pitch. Such distillates include distillate cylinder stocks having a flash point in the neighborhood of 525 F., leaving a pitch residue.

In the commercial practice of dewaxing procemes, the wax-containing oil is treated prior to dewaxing by steps which vary in accordance with the characteristics of the oil to be dewaxed. Oil fractions which contain wax which precipitates in crystalline form are dewaxed by filter-pressing, in a chilled state, a solution of the oil which is formed by adding naphtha or as the result of naphtha or gas oil present by reason of the steps leading to the production of the fraction to be dewaxed. Oil fractions that are to be dewaxed by filter-pressing are separated from crude petroleum by distillation, and it is not important that cracking be avoided since cracking increases the crystallinity of the wax precipitated by chilling. Oil fractions that are to be dewaxed by methods suitable to the removal of amorphous wax, such as methods dependent upon difference of specific gravity and particularly centrifugal separation, are separated from crude petroleum as either a distillate or a residue by distillation so carried out as to minimize or eliminate cracking, as by the use of the lowest possible temperature and the use of vacuum or steam in large quantities or the use of both vacuum and steam. Other vapors, or substances which vaporize during the distillation may be used to reduce or eliminate cracking such as CO2, nitrogen, fixed gases from petroleum or lower boiling liquid fractions of petroleum, e. g.,

gas oil. If the oil to be dewaxed, which maybe a distillate or a residue of petroleum or even petroleum itself, has a color darker than that required by commercial specifications, which is the case with substantially all oil except possibly some fractions of Cabin Creek petroleum, the oil to be dewaxed is subjected to treatment to improve its color and especially to remove hard 'asphalt before dewaxing. This step has been practiced since the inception of dewaxing. This purification is eflected by means of such common refinery expedients as distillation, treatment with sulphuric acid and treatment with clay, in such manner as to avoid injury to the oil and such alteration of the wax as would impair the effectiveness of the steps taken for the removal thereof. Fractions to be dewaxed by methods suitable to the removal of amorphous wax have usually been brought to a color that meets commercial requirements prior to dewaxing. One exception is that in accordance with a more recently developed practice these fractions may be, as hereinafter referred to, dewaxed while they retain undesirably dark color if they contain crystalline wax that would otherwise impair the effectiveness ofsteps taken for the removal of wax. Other possible exceptions are that in the older days of cold settling some refiners acid treated and neutralized topped crude, i. e., crude from which the naphtha and kerosene had been removed by distillation, then further distilled to a cylinder stock residue and cold settled this cylinder stock and finally brought the cold settled cylinder stock to a final color by percolation through clay; and other refiners used much the same procedure except that they percolated the cylinder stock through clay before dewaxing by cold settling rather than afterwards. with the development of the centrifugal dewaxing of cylinder stock practically all of the cylinder stock was percolated to final color prior to centrifugal dewaxing. It is now common practice to reduce the crude all the way to cylinder stock and do the acid treating on the cylinder stock residue, neutralize and bring to final color by contacting withclay and then centrifugally dewax.

Referring more particularly to oil fractions that are to be dewaxed by methods suitable to the removal of amorphous wax, and particularly by centrifugal dewaxing, the variations in the steps in the treatment of the oil prior to dewaxing are readily chosen in the light of refinery experience. If the oil fraction to be dewaxed contains a quantity of asphalt so great that it would be uneconomical to attempt to remove it by acid treatment or by clay treatment, or by both treatments, as

in the case of residues of some mixed base crude petroleums, it is distilled, without cracking, as by distillation with vacuum or liberal amounts of steam or both, leaving most of the asphalt in the residue. If the resulting distillate, or any other distillate or any residue which is not distilled prior to dewaxing, contains an anmunt of asphalt which will impair the dewaxing operation and which can not be economically removed by clay treatment, it is subjected to acid treatment in which, for example, the oil is agitated with concentrated sulphuric acid, as by means of air agitation, and the resulting sludge is removed, as by gravity settling. Ordinarily such a proportion of acid is used that the oil is thereby, in conjunction with subsequent operations, brought to satisfactory color and stability. Ordinarily the acid treatment is carried out at as low a temperature as possible but at a temperature high enough to reduce the viscosity of the oil sufficiently to facilitate the reaction between the oil and the acid and the settling of the sludge. Obviously, the acid treating is so controlled as to eliminate or minimize losses of and injury to the oil or constituents thereof, to'cause the operation, to proceed properly and efiectively and to avoid any alteration of the oil or of constituents thereof that will interfere with or impair subsequent treatments of the oil such as neutralizing or dewaxing. To this end the proportion of acid, intensity and duration of agitation, time of settling or other separation, and temperature attained, are all ascertained by experiment in the light of experience. In effecting the desired purifying reaction by the acid the occurrence of the so-called secondary reaction must be eliminated or minimized by careful control of these features of operation. Thus temperatures between 110 F. and 140 F. may be utilized as by treatingthe 49 oil at a temperature of approximately 120 F. but temperatures as high as 195 F. have been satisfactorily employed in acid treating cylinder stocks prior to dewaxing especially when the other features of control of the acid treating are suitably regulated.

The required acid may be added to thedifby separately adding fractions of the total amount of acid employed, such treatment with fractional parts of the total acid used being known as 50 dumps. Various expedients, such as addition of small quantities of water, have been resorted to as an aid to the separation of the sludge from the oil. The resulting sour oil recovered by gravity separation from sludge, is

blown with air to remove sulphur dioxide. The blown oil is then neutralized and decolorized with clay. Oil may be acid treated while undiluted, partially diluted or completely diluted for dewaxing. It may be neutralized with caustic alkali or ammonia or by high temperature contacting with clay; and it may be further decolorized by high temperature contacting with clay, percolation at a high temperature through clay or percolation at a low temperature while diluted through clay. When clay is used by percolation,

alkali or ammonia must be used for neutralization. When oil is neutralized and decolorized by high temperature contacting, acid treatment will not be done with the oil in solution. For

example, the undiluted, blown, sour oil is mixed with finely divided clay, either in dry form or mixed with water and existing in the form of a mud, and the mixture is heated to drive off moisture and promote reaction of the clay with the oil, the temperature being raised to a temperature, e. g., between 400 F. and 600 F., sufllciently high to obtain the necessary neutralizing and purifying effect of the clay but kept as low as possible in order to avoid injury. to the oil and such alteration of the wax as would impair the efiect of the dewaxing operation. Thereafter the mixture of oil and clay is cooled and blended with all or with a part of the naphtha necessary for subsequent dewaxing operation; and the'mlxture is then passed through filter presses to remove the spent clay while being kept at a temperature e. g., F. to F., sufiiciently high that there is no cloud in the oil other than such cloud as may be due to the presence of the clay. The clay treatment neutralizes the sour oil and effects additional improvement in the color. In lieu of the above mentioned contacting of the sour oil with clay at elevated temperature, the oil may be neutralized with alkali as by agitation with an aqueous solution of caustic soda, separated from the residual solution, washed with water, and percolated through granular clay at a temperature in the neighborhood of 300 F.; or the sour oil may be neutralized with alkali, as by agitation with an aqueous solution of caustic soda, separated from the residual solution, washed with water, diluted with a solvent, and percolated through granular clay at a temperature above that at which a cloud forms in the oil; or the dark oil may be first diluted with the solvent, acid treated as above described, neutralized with alkali, as by agitation with an aqueous solution of. caustic soda, washed with water and percolated through granular clay at a temperature above that at which a cloud forms in the oil. Thus, the oil is brought to the final color required by commercial specification unless the recent development above referred to is followed, in which case the oil is brought to a color that is darker but facilitates dewaxing of oils which contain crystalline wax, such as long residues, and distillates which also contain amorphous wax.

The foregoing preliminary steps are modified in accordance with the nature of the oil to'be dewaxed, but in any case oil that is to be dewaxed centrifugally must be substantially freed of asphalt that precipitates when the oil is diluted with naphtha and of impurities which prevent the complete precipitation of the wax. In some cases the distillation of the oil for the purpose of leaving asphalt in the residue, may be omitted, as in the case of some residues of mixed-base crude petroleums. In some cases the acid treatment of the oil may be omitted and the oil may simply be clay treated as above described before dewaxing, as in the case of fractions of Pennsylvania oils. Some oils require neither acid treatment nor clay treatment before dewaxing, as in the case of some fractions of Cabin Creek oils.

In commercial practice of centrifugal dewaxing, the oil to be dewaxed, having a color suitable to final color requirements or having a darker color for the purpose of facilitating dewaxing, or having been brought to such color by a. suitable variation of the procedure above described, is diluted with naphtha or further diluted therewith, as may be necessary, to the end that the solution consists of 75% to 60% of naphtha having a specific gravity of 55 A. P. I. to 70 A. P. I. The solution is then chilled in such manner as to avoid shock-chilling that would give faulty precipitation of the wax, as by proceeding in accordance with the method of my Patent No. 1,558,619, preferably reducing the temperature of the solution at the rate of 2 F. to 3 F.

g per hour, at least until the temperature is in the neighborhood of -10 F., after which the chilling may be more rapid and so-called shockchilling maybe used. The chilling is continued until the mixture attains a temperature, e. g., between F. and -40 R, which gives a sufficiently complete precipitation of wax to produce dewaxed oil having the desired A. S. T. M. pour test and cloud test. it being found that the more extensive the chilling the lower will be the final cloud test and the lower will be the A. S. T. M. pour test down to the minimum indication, determined by viscosity, which is obtainable by that test. The chilled oil is then separated from the precipitated wax by continuous centrifugal separation. -The naphtha is removed by steam distillation and resulting residue consists of finished lubricating oil of reduced cold test and desirable color which is divided by distillation into fractions having viscosities and fire tests meeting commercial specifications.

Relatively recent developments of the foregoing commercial procedure in centrifugal dewaxing, are described in my Patents No. 1,784,525

and No. 1,881,643. Patent No. 1,784,525 describes a dewaxing process wherein there is caused to be present in he oil to be dewaxed, by addition or otherwise, bituminous substances such as impurities other than hard asphalt and naturally contained in petroleum oils and removable therefrom by clay or acid treatment, for the purpose of causing wax in the oil to precipitate in a form suitable for centrifugal removal even when crystalline wax is present. This is the development above referred to wherein the oil is dewaxed while it has a color darker than the color commercially desired, instead of being brought to commercial color before dewaxing as in the older practice which still applies to cylinder stock residues and residues of 450 F., and higher, flash point and high viscosity distillates. of over 450 F. flash. Patent No. 1,881,643 describes the addition to the wax-containing oil prior to dewaxing thereof, of amorphous wax, or of amorphous wax and bituminous products such as impurities other than hard asphalt and contained in petroleum and removable therefrom by clay treatment, for facilitating continuous centrifugal dewaxing of the oil. The use of these modifications enables the centrifugal dewaxing of petroleum fractions which contain wax that would preoipitate in crystalline form if isolated, including distillates and including residues having flash points below 450 F. and as low as 350 F.

While substantially all of the low cold test lubricating oils manufactured in this country have been during the past several years and are now produced in accordance with the foregoing procedure, I have found that in the dewaxing of some of the oils above referred to, particularly fractions of lower flash point and o ls slightly cracked in separating them from the crude petroleum, and fractions including residues obtained from wax-containing petroleums of high asphalt content, the wax in the centrifugal rotor becomes insufficiently plastic at certain points and impairs or stops the continuous centrifugal separation of precipitated wax from the oil, and/or the dewaxed oil may acquire, upon standing, a cloudiness which is not identical with the cloud formed .by chilling the oil as in the A. S. T. M. cloud test but is a fluffy, soft, hazy cloud occurring at temperatureseven as high as ordinary temperatures, e. g., 72 F., and capabl'e of being dispersed but not eliminated by agitation of the oil and incapable of being removed by ordinary illtration. In other words, I have found that in the dewaxing of certain oils in accordance with the foregoing procedure, the wax in the centrifugal rotor, which has been separated from the oil but not yet discharged from the rotor, acquires at certain points in the rotor a hardness which impairs the separation of the wax and its discharge from the rotor, for example, at the outer edge of the disc which divides the main separating compartment of the rotor from the compartment that contains auxiliary or carrier liquid and through which wax passes to its discharge point; and I have found that even though the dewaxing operation has involved chilling to 30 F. prior to centrifugal dewaxing and the resulting dewaxed oil has an A. S. T. M. pour test in the neighborhood of 0 F., and at even 30 F. develops no cloud in the A. S. T. M. cloud test, that dewaxed oil may nevertheless possess or acquire upon standing, at temperatures as high as 72 F. the haziness or cloudiness above referred to.

A feature of this invention is that in the dewaxing of fractions of wax-containing petroleum, the oil is subjected to a treatment which effects such alteration of the oil or of constituents thereof that such hardening of the wax in the rotor and such formation of a hazy cloud in the dewaxed oil do not occur. I do not attempt to explain the exact effect of such treatment other than to state that the result of the treatment is that the deleterious hardening of the wax in the rotor and the occurrence of such a hazy cloud are avoided, but the effect may be an alteration of the oil or of some constituent thereof and it is my present belief that the effecting of the treatment consists in the removal of some constituent or constituents not fully identified but which tend to cause such hardening of the wax and to cause the appearance of such a hazy cloud. As a specific example of the treatment of waxcontaining oil in accordance with this invention for the purpose of overcoming the undesirable hardening of the wax and the formation of such a hazy cloud, the oil is mixed with finely divided solids and is diluted and the mixture is brought without shock-chilling to a temperatureie. g., between 50 F. and 75 F.) sufliciently low to form in the oil a cloud other than that due to the added solids and sufficiently high to avoid such extensive precipitation of amorphous wax as would impair or clog the subsequent filtration of the oil, and then the mixture is filter-pressed to remove solids therefrom such as added solids and precipitated solids or semi-solids in which precipitated wax may be present. This treatment, especially if carried out prior to the centrifugal dewaxing of the oil, may result in some precipitation of wax prior to filter-pressing and such precipitated wax is removed with the other solids in the filter-pressing operation. This treatment may be applied to the oil either before or after centrifugal dewaxing thereof, and in connection with the centrifugal dewaxing above described it results in an elimination of the occurrence of the cloudiness at relatively high temperatures, e. g., 72 F., and if it is carried out prior to the centrifugal separation it also results in the avoidance of the formation within the centrifugal rotor of hard bodies of wax that impair or stop the continuous centrifugal separation of precipitated wax from the oil.

In the practice of this invention the treatment of the wax-containing oil with finely divided solids is preferably carried out prior to the cen- -trifugal dewaxing operation. Substantially neutral solids which may be used are kieselguhr, s sawdust, paper pulp and similar neutral solids. When such solids are used they are added to a solution of the wax-containing oil, in which naphtha may be the solvent, in the proportion of .25 pound to 1.0 pound per gallon of oil present in the solution.

, It is a further and important feature of my invention that the treatment of the wax-containing oil by finely divided solids, to effect in accordance with this invention the treatment which effects the elimination of the cloudiness at ordinary temperatures and the occurrence of hard bodies of wax in the centrifuge, may be effected by modification of the ordinary centrifugal dewaxing process above described. To this end it is a feature of this invention that when the waxcontaining oil is subjected to clay treatment for the removal of asphalt or for the improvement of the color of the oil or for the neutralization of the oil subsequent to acid treatment, or for any two or more of these purposes or for other purposes, the wax-containing oil having the clay mixed with it is cooled, prior to the removal of the clay by filter-pressing, diluted and then further cooled to a temperature (e. g. between 50 F. and 75 F.) which is substantially lower than the temperature (e. g. 130 F. to 140 F.) at which spent clay has heretofore been removed from oil prior to dewaxing and sufficiently low to cause the treatment of the oil with the finely divided 86 solids and the filter-pressing of the solids therefrom to effect an avoidance of the hazy cloud and the hardening of wax in the rotor, and then the clay and any precipitated wax and other solids are removed by filter-pressing. In the procedure last described it is apparent that the clay serves bothto neutralize sour oil or to improve color or to effect both of those results and also to eliminate the causes of the hazy cloud in the oil and hardening of the wax in the centrifuge. In addition the oil is centrifugally dewaxed in an operation in which it is chilled without shock-chilling at such temperature as will impart to the dewaxed oil the finally desired cold test and cloud test.

In the practice of this invention, the cooling of the mixture of wax-containing oil and decolorizing or neutralizing clay or other finely divided solids, prior to the filtration that removes such solids, to a temperature that effects avoidance of hazy cloud and hardening of wax in the rotor, may, and probably will, if carried out prior to the centrifugal dewaxing, cause some precipitation of wax, but the cooling and filtering is not primarily a dewaxing step and is at most an auxiliary to the centrifugal dewaxing; and the cooling should not be carried so far as to cause precipitation of amorphous wax to an' extent suflicient to clog or impair the filter-pressing operation, or to require addition of a large proportion of solids to 5 prevent clogging in the filter-pressing operation, by which there are removed from the oil the clay or other finely divided added solids and other solids including any precipitated wax.

In centrifugal dewaxing there is ordinarily no difiiculty in carrying out the continuous centrifugal separation of precipitated wax when the oil to be dewaxed is given suitable preliminary treatment, particularly treatment for the removal of hard asphalt (asphalt which is precipitated in oil upon addition of naphtha thereto and is brittle),

and the oil consists of a residue having a flash point in the neighborhood of 500 I". to 550 F., such bodies of oilbeing commonly referred to as steam-refined cylinder stock which after decolorization and dewaxing is known as bright stock. 5 The wax in such fractions is so-called amorphous wax. As the flash point of the oil fraction to be dewaxed becomes lower and lower as a result of the fact that less and less of the lighter constituents of the petroleum are distilled ofl, the propor- 10 tion of wax in the oil which would precipitate in crystalline form, if isolated, becomes greater and greater and the probability of cloggage of the rotor increases and the separation of the wax from the oil becomes less complete even though the total wax present includes a large proportion of wax that would precipitate in the so-called amorphous form in the absence of such crystalline wax. It is usually only possible to carry out continuous centrifugal separation of precipitated wax in connection with residues having a flash point of 425 F. or higher and in connection with distillates having a fiash point in the neighborhood of 425 F. or higher and leaving a pitch residue. However, as pointed out in my Patent No. 1,784,- 525, difficulties in continuous centrifugal separation of wax due to the presence of crystalline wax, as, for example, in the case of such fractions, may be minimized, to such extent that fractions having a flash point as low as 350 F. may be dewaxed by continuous centrifugal separation, by dewaxing the oil while it still contains or after it has had added to it bituminous substances such' as substances other than hard asphalt which are commonly removed from petroleum by clay treatment; and difficulties due to the same causes may be minimized by the addition of amorphous wax such as petrolatum, with or without the presence of such bituminous substances, as described in my copending application above mentioned.

In the practice of this invention the treatment of the oil with finely dividedsollds to eliminate the causes of the hazy cloud and the hardening of wax (either solids added solely for that purpose or clay present. in the oil for effecting other results in addition), is carried out in conjunction with the centrifugal dewaxing operation described; and it is to be noted that the lowering of the A. S. T. M. pour test and cloud test of the final oil may be said to be a function of the degree to which the solution of wax-containing oil is chilled prior to centrifugal separation of the precipitated wax, and that such chilling may be carried to temperatures as low as F. The constituents of wax-containing oil which cause the faint cloudiness or haziness at ordinary temperatures and which tend to form hard accumulations in the rotor of the centrifugal machines, and which are removed or rendered ineffective to produce these results by the treatment of oil with finely divided solids in accordance with this invention, appear to be comparatively insoluble in a solution of the oil in naphtha which is prepared for the centrifugal dewaxing operation, and they appear to precipitate at higher temperatures than the temperatures at which the amorphous wax present in the oil precipitates and to precipitate before precipitation of the amorphous wax occurs. They appear to precipitate either as hard crystals which interfere with continuous discharge of amorphous wax from the rotor of the centrifuge or as microscopic crystals which are not readily separable from the naphtha-oil mixture during the centrifugal separation of precipitated amorphous wax therefrom. These constituents may impair or stop centrifugal separation of precipitated wax and prevent the attainment of the desired low cold test, or cause the slight cloudiness or haziness referred to, even though desirably low A. S. T. M. pour and cloud tests are obtained. I have discovered that if the solids which are filtered from the oil at 70 F. or thereabouts are washed with naphtha at the same temperature to remove oil and then further washed with naphtha at a temperature of approximately 125 F., this high temperature washing will extract from those solids a hard high melting point substance somewhat similar to ozocerite or carnauba wax. This extracted material is of a yellow color with a melting point of 170 F. or higher. It is unusually hard.

Specific examples of the practice of this invention, to which this invention is not limited, are as follows:

A. Along residuum having a flash point of about 350 F. is produced from Pennsylvania crude petroleum by batch distillation in shell stills with fire and steam, the distillation being carried to a temperature in the neighborhood oi. 500 F., and the resulting residue being a long residue having a viscosity in the neighborhood of 55 seconds at 210 F. For the purpose of removing hard asphalt and improving the color of the oil it is contacted with finely divided clay in the proportion of one pound of clayto each gallon of oil and the mixture is heated to a temperature between 400 F. and 500 F. and brought to desired color. Thereafter the mixture is cooled to about 130 F. at which point naphtha having a temperature of about 100 F. and having a boiling range of 160 F. to 320 F. is added until the mixture consists of about 35% oil and 65% naphtha. Thereupon the mixture is cooled to 70 F. without shock-chilling at the rate of 2 F.'to 3 F. per

hour with mild stirring and then subjected to filter-pressing to remove the clay and such wax and other solids as'are thereby precipitated. The filtrate is cooled to about 30 F. to 40 F. without shock-chilling and then subjected to continuous centrifugal separation and the resulting wax-freed oil-naphtha solution is steam distilled to remove the naphtha, producing a final oil of which the approximate characteristics are:

Flash point 350 F. Fire test 425 F. Saybolt viscosity 50 seconds at 210 F. Pour test 5 F. Cloud test '40 F. Color 5 N. P. A.

By the ordinary procedure first above described this same oil produced a dewaxed oil having a pour test and cloud test of about 30 F., the high pour test and cloud test being due to the presence during centrifugal dewaxing of constituents capable of hardening wax in the rotor and causing hazy after-cloud.

B. From mixed-base Mid-Continent crude petroleum, a residue having a flash point of about 350 F. is obtained by batch distillation in a shell still with fire and steam, the distillation being carried to a temperature in the neighborhood of 500 F. and the residue being a long residue having a viscosity in the neighborhood of 70 seconds at 210 F. The residue is acid treated as above described with 30 pounds of 66 B. sulphuric acid to each barrel of oil, the mixture being maintained at a temperature approximating but not in excess of 130 F., and air blowing being maintained for 30 minutes to eflect agitation of the acid and oil. After blowing is stopped the oil is allowed to settle for twelve hours and the resulting sludge removed. Thereafter the oil is blown for 20 minutes to effect removal of sulphur dioxide. Thereafter the oil is contacted with clay in the proportion of 0.7 pound of clay per gallon of oil and the mixture is heated to a temperature between 400 F. and 500 F. and brought to a final desired color. treated oil is then cooled to approximately 130 F. and the remaining treatment of the oil is the same as that applied to the oil in Example A after the temperature of that oil is reduced to 130 F. following the clay treatment thereof. As a result the dewaxed oil has the following approximate characteristics:

Flash point 350 F. Fire test 425 F. Viscosity 55 seconds at 210 F. "Pour test 0 F. Cloud test 40 F. Color 5 N. P. A.

The acid treated and clayresidue of brittle pitch, a cylinder stock distillate having a flash point of about 525 F., a fire test of about 600 F. and a Saybolt universal viscosity of 150 seconds at 210 F. This distillate is acid treated with about 15 pounds of 66 B. sulphuric acid per barrel of oil while maintaining the temperature approximate to but not above 140 F. and carrying on agitating blowing for 30 minutes. After settling for about 12 hours sludge is removed and the oil is blown for about 20 minutes for removal of sulphur dioxide. Then the oil is contacted with about 0.8 pound of clay per gallon of oil at a temperature between 400 F. and 500 F. and the mixture is cooled to about 130 F. Thereafter the treatment of this oil is the same as the treatment of the oil in Example A after the cooling of that oil to 130 F. following the clay treatment thereof. As a result of this treatment oil having the following approximate characteristics is produced:

Treatment of this oil in accordance with the older centrifugal dewaxing method first above described produces an oil that develops a hazy cloud after standing 24 hours and that cloud does not disappear unless the oil is heated to about 90 F. The cloud is not the same as that which occurs in the A. S. T. M. cloud test but is a fiuify, hazy cloud which forms at so-called room temperature, e. g., 70 F., 24 hours after the oil has cooled down.

D. From mixed-base Mid-Continent crude petroleum there is produced by distillation with a similar pipe still and fractionating tower, leaving a pitch residue, an amorphous-wax-containing distillate having a flash point of about 400 F. and a Saybolt universal viscosity of about 65 seconds at 210 F. This distillate isacid treated with Y rel of oil while maintaining the temperature approximate to but not in excess of 130 F., agitating blowing being carried on for 30 minutes. After 12 hours settling, the sludge is removed and the oil is blown for 20 minutes for sulphur dioxide removal. Then the oil is treated with about 0.4 pound of clay per gallon of oil at 400 F. to 500 F. and then cooled to 130 F. after which it is subjected to the same treatment as that applied to the oil in Example A after that oil is cooled to 130 F. following the clay treatment thereof. The resulting oil has the following approximate. characteristics:

Flash point 400 F. Fire test 475 F. Viscosity 60 seconds at 210 F. Pour test 0 F. Cloud test 40 F. Color 5 N. P. A.

An attempt to dewax this oil by the older centrifugal dewaxing process as above described would result in a clogging of the rotor of the centrifuge by hard wax.

E. From mixed-base Mid-Continent crude petroleum there is obtained by distillation with a similar pipe still and fractionating tower, leaving a residual fraction having a flash point of 525 F., a wax-containing distillate having a flash point of about 400 F. and a viscosity of about 500 seconds at F. This fraction is acid-treated with about 7 pounds of 66 B. sulphuric acid per barrel of oil at aproximately F. with agitating blowing for about 30 minutes. After 12 hours settling the sludge is removed from the oil and the oil is blown for about 20 minutes to remove sulphur dioxide and then contacted with about 0.4 pound of clay per barrel of oil at 400 F. to 500 F. The acid treated and clay treated oil is then cooled to F. and subjected to the same treatment as that to which the oil in Example A is subjected after being cooled to 130 F. following the clay treatment thereof. The resulting oil has the following approximate characteristics:

Flash point 400 F. Fire test 475 F. Viscosity 475 seconds at 100 F. Pour test 0 F. Cloud test -40 F. Color 3 N. P. A.

In the foregoing examples there was no clogging of the centrifugal rotor and no hazy cloud formed in the final products. While the dewaxed oil'produced in the foregoing examples ceased to flow in accordance with the procedure of the A. S. T. M. pour test at the temperatures given for the pour test, that condition was due to the viscosity of the oil at that temperature and not due to its solidification by reason of the presence of wax, there being no abrupt change at the stated pour test temperature in the rate at which the viscosity of the dewaxed oil changes with temperature, the oil being completely liquid down to temperatures far below 0 F. Thus, the maximum reduction of pour test temperature by removal of wax was effected, the pour test being reduced to the minimum that is determined by the viscosity of the oil in the A. S. T. M. poun test.

Inasmuch as this invention applies to residues and distillates, it will be apparent that lubricating oils, suitable for various specific uses and having any possible boiling range and any possible viscosity can be produced either by splitting up the dewaxed product in accordance with general refinery procedure or by obtaining from crude petroleum a fraction having the viscosity desired in the final product and then dewaxing that fraction to produce directly a low pour test and low cloud test 011 that will not acquire a haze at ordinary temperatures and which possesses the viscosity desired in the final product. Possible exceptions to the foregoing procedure are oils now commonly produced by forming a fraction containing only crystalline wax and dewaxing that fraction as far as possible by filter-pressing. However, practice in accordance with this invention results in the removal or the rendering ineffective of those constituents of the crude petroleum which tend to cause the dewaxed oil to haze at ordinary temperatures and tend to cause hardening of wax in the rotor. Inasmuch as removal of clay added for decolorizing or neutralizing or removal of other added finely divided solid material is carried out in accordance with this invention at a temperature which may be and preferably is reduced as far as it can be reduced without causing such precipitation of amorphous wax as will impair the filtering by which the clay or other solid is removed, the removal of substantial proportions of crystalline wax may occur, and usually does occur in the treatment of residues and distillates having a flash point below 450 F., in the filter-Dressing operation by which there are removed from the oil the added solids and precipitated and other solids or semi-solids including any such wax. This facilitates the continuous centrifugal dewaxing of residues and distillates containing lower boiling constituents and having lower viscosities,'e. g., residues having a flash test below 350 F., and distillates to pitch residue and having a flash test below 400 F. Therefore, by this invention it is possible to produce a dewaxed product that will give by distillation a fraction having a lower viscosity than the first distillate from products centrifugally dewaxed heretofore. Moreover, the lower boiling distillates from products heretofore dewaxed usually have a higher pour test than that of the entire dewaxed product or of the higher boiling or higher viscosity constituents of the whole dewaxed product, but the pour test of the first distillate of the product dewaxed in accordance with this inventionhas a pour test which is little, if any, higher than that of the whole dewaxed product. Thus, there may be dewaxed by this invention a residue having a flash point as low as 350 F. or lower, or a distillate that contains constituents similar to the lower viscosity constituents of such residue, and after dewaxing there may be obtained therefrom by distillation oils for special uses having a viscosity of 120 seconds at 100 F. and a. cold test of 0 F. to 10 F. and also oils having higher viscosities. Thus, fractions having successively higher viscosities up to 200 seconds at 210 F. and similarly low cold tests are obtainable from the dewaxed oil if it is a residue or a distillate carried to a brittle pitch residue, although the yield from such distillates of oils having a viscosity in excess of seconds at 210 F. will be small. In addition to the foregoing identification of bodies of oil which yield a dewaxed oil, when dewaxed in accordance with former practice and without the use of this invention, which may be clear when first dewaxed but which acquire a hazy cloud upon standing under atmospheric conditions, it

may be noted that practically all .distillates dewaxed by continuous centrifugal dewaxing will possess such a cloud, that residues which areso long or have such low flash point that the initial fraction distilled therefrom will have a viscosity of 50 will in practically all instances possess such a cloud, and that residues of such high flash point that the initial fraction distilled therefrom will possess a viscosity of 70 at 210 F. may possess a cloud but are likely to be free of such a cloud.

I claim: a

1. In the production of dewaxed mineral oils from mineral oil containing wax of which a substantial proportion is amorphous in character,

the steps comprising mixing the wax-containing oil with finely divided solids and. a solvent and' filtering the mixture to remove the added and precipitated solids at a temperature low enough to form in the oil a cloud other than that due to the added solids and sufllciently high to prevent substantial precipitation of amorphous wax, and cooling to a substantially lower temperature a solution of the filtered oil and removing precipitated wax from the cooled solution by continuous centrifugal separation.

2. In the production of dewaxed mineral oil from mineral oil containing wax of which a substantial proportion is amorphous in character, the steps comprising mixing the wax-containing oil with finely divided solids and a solvent and filtering the mixture at a temperature between 50 F.

and 75 F. to remove solids therefrom, and cooling to a substantially lower temperature a solution of the filtered oil and removing precipitated wax from the solution by continuous centrifugal separation.

3. In the dewaxing of mineral oil, the steps comprising mixing with a solvent and finely,divided solids a mineral oil containing wax of which a substantial proportion is amorphous in character and of the group consisting of a wax-containing petroleum residue having a flash point of approximately 350 F. to 450 F., awax-containing petroleum distillate having a flash point of approximately 400 F. to 525 F. and obtained by distilling the petroleum to a pitch residue, and a wax-containing petroleum distillate having a flash point of approximately 400 F. and obtained by distilling the petroleum to a residue having a flash point of approximately 525 F., filtering the mixture to remove added and precipitated solids at a temperature low enough to form in the solution a cloud other than that due to the added solids and sufiiciently high to prevent such precipitation of amorphous wax as will impair filtering of the mixture, cooling to a substantially lower temperature a solution of the filtered oil, and removing precipitated wax from the cooled solution by continuous centrifugal separation.

4. In the production of dewaxed mineral oil from mineral oil containing wax of which a substantial proportion is amorphous in character, the steps comprising mixing the waxcontaining oil with finely divided solids and. a solvent, bringing the mixture to a temperature sufflciently high to cause all of the wax in the oil to be in solution, then cooling the mixture to a temperature sufficiently low to form in the oil a cloud other than that due to the added solids and sufiiciently high to prevent substantial precipitation of amorphous wax and filtering the cooled mixture to remove solids, and chilling a solution of the filtered oil to a substantially lower temperature and removing precipitated wax from the chilled solution by 75 continuous centrifugal separation.

5. In the production of dewaxed mineral oil from mineral oil containing wax of which a substantial proportion is amorphous in character, the steps comprising mixing the wax-containing oil with finely divided solids and a solvent, bringing the mixture to a temperature sufilciently high to cause all of the wax in the oil to be in solution, then cooling the mixture to a temperature between 50 F. and 75 F. and filtering the solids therefrom, and chilling a solution of the filtered oil to a substantially lower temperature and centrifugally separating precipitated wax therefrom.

6. In a method for producing dewaxed mineral oil from mineral oil containing wax of which a substantial proportion is amorphous in character which includes diluting, chilling and centrifugal separation of precipitated wax, the steps comprising adding finely divided solidsto a solution of the wax-containing oil and filtering out the solids at a temperature sufilciently low to form in the oil a cloud other than that due to the added solids and sufilciently high to prevent substantial precipitation of amorphous wax, prior to chilling the oil to a temperature at which it is to be subjected to centrifugal treatment.

7. In the production of dewaxed mineral oil from mineral oil containing wax of which a substantial proportion is amorphous in character, the steps comprising adding finely divided clay and a solvent to the wax-containing oil and filtering the resulting mixture to remove solids therefrom at a temperature sufilciently high to prevent substantial precipitation of amorphous wax and sufliciently low to cause a cloud in the oil other than that due to the solids, and chilling a solution of the filtered oil to a substantially lower temperature at which centrifugal separation will give oil of desired low cold test and removing precipitated wax from the chilled solution by con- .tinuous centrifugal separation.

8. In the production of dewaxed mineral oil from mineral oil containing wax of which a substantial proportion is amorphous in character, the steps comprising adding finely divided clay to the oil and heating the clay-containing mixture to temperatures between 400 F. and. 600 F., then filtering a solution of the clay-containing oil cooled to a temperature low enough to form in the oil a cloud other than that due to the added solids and high enough to prevent substantial precipitation of amorphous wax, and chilling a solution of the oil to a temperature low enough to cause oil recovered by centrifugal separation to have the desired low' cold test and removing precipitated wax from the chilled solution by continuous centrifugal separation.

9. In the production of dewaxed mineral oil from mineral oil containing wax of which a substantial proportion is amorphous in character, the steps comprising adding finely divided clay to the oil and heating the clay-containing mixture to a temperature between 400 F. and 600 F. cooling the mixture to a temperature between 160 F. and a temperature at which wax begins to form a cloud in the oil, adding a solvent to the cooled oil and bringing the resulting mixture -to a temperature'at which it contains a cloud produced by the cooling, but not sufilciently low to cause substantial precipitation of amorphous wax, filtering solids from the cooled mixture, and then further chilling a solution of the filtered oil and removing precipitated wax therefrom by continuous centrifugal separation.

10. In the producton of dewaxed mineral oil from mineral oil containing wax of which a sub- 'stantial proportion is amorphous in character, the steps comprising acid treating wax-containing mineral oil with sulphuric acid, removing resulting sludge, adding finely divided clay to the sour acid treated oil and heating the mixture to a temperature between 400 F. and 600 F., cooling the resulting mixture, adding a solvent to the 10 mixture and bringing the mixture to a temperature sumciently low to form in the oil a cloud other than that due to the added solids and sufficiently high to prevent such precipitation of amorphous wax as will impair the filtering of the mixture, filtering solids from the mixture, and then further cooling a solution of the filtered oil and centrifugally removing precipitated wax therefrom.

11. In the production of dewaxed mineral oil from mineral oil containing wax of which a substantial proportion is amorphous in character, the steps comprising treating wax-containing mineral oil with sulphuric acid at a temperature between 115 F. and 140 F., removing resulting sludge, contacting the sour acid treated oil with finely divided clay at a temperature between 400 F. and 600 F., filtering solids from a solution of the clay treated oil at a temperature sufiiciently low to form in the: oil a cloud other than that due to the clay and sumciently high to prevent substantial precipitation of amorphous wax, then cooling a solution of the filtered oil to a temperature between 20 F. and '70 F. at a rate sufficiently low to avoid shock-chilling of the mixture, and centrifugally removing precipitated wax from the solution.

12. In the production of dewaxed mineral oil from mineral oil containing wax of which a substantial proportion is amorphous in character, the steps comprising contacting acid-treated wax-containing mineral oil with finely divided clay to effect neutralization, and filtering a solution of the resulting mixture at a temperature sufliciently low to' formin the oil a cloud other than that due to the added solids and sufiiciently high to prevent substantial precipitation of amorphous wax present, and then centrifugally removing precipitated wax from a chilled solu tion of the resulting oil.

50 13. In the production of dewaxed mineral oils from mineral oil containing wax of which a substantial proportion is amorphous in character,

the steps comprising mixing the wax-containing oil with finely divided solids and a solvent and filtering the mixture to remove the added and precipitated solids at a temperature low enough to form in the oil a cloud other than that due to the added solids and suificiently high to prevent substantial precipitation of amorphous wax, 60 and, after the oil has been freed by said filtering operation of solids which impair continuous centrifugal separation of precipitated wax, cooling to a substantially lower temperature a solution of the oil and removing precipitated wax 65 therefrom by continuous centrifugal separation. 14. In the production of dewaxed mineral oil,

the steps comprising forming a mixture of finely divided solids and a solvent and oil containing crystalline wax and amorphous wax; separating from the mixture,.while the mixture is at a temperature low enough to precipitate crystalline wax and to form in the oil a cloud other than that due to the finely divided solids and sufficiently high to prevent substantial precipitation of amorphous wax, said finely divided solids and solids precipitated therein; cooling a solution of the oil separated from said finely divided and precipitated solids to a temperature at which wax precipitates therein; and'removing said precipitated wax from the cooled solution by a method suitable to the removal of precipitated amorphous wax therefrom.

15. In the production of dewaxed mineral oil,

the steps comprising forming a mixture of a solvent and oil which has been contacted with finely divided clay to improve the color thereof and contains amorphous wax and crystalline wax and a substantial proportion of said clay; separating from the mixture, while the mixture is at a temperature low enough to form in the oil a cloud other than that due to the clay and sufficiently high to prevent such precipitation of amorphous wax as will impair filtering of the mixture, said clay contained therein and solids that are precipitated therein; cooling a solution of the oil separated from said solids to a temperature at which wax precipitates therein; and removing said precipitated wax from the cooled solution by a method suitable to the removal of precipitated amorphous wax therefrom.

16. In the production of dewaxed mineral oil, the steps comprising forming a mixture of a sol-- vent and oil which has been contacted with finely divided clay to improve the color thereof and contains amorphous wax and crystalline wax and a substantial proportion of said clay; separating from the mixture, while the mixture is at a temperature low enough to precipitate crystalline wax and to form in the oil a cloud other than that due to the clay and sufficiently high to prevent such precipitation of amorphous wax as will impair filtering of the mixture, said clay contained therein and solids that are precipitated therein; cooling a solution of the oil separated from said clay and solids to a temperature at which wax precipitates therein; and removing precipitated wax from the cooled solution by a method suitable to the removal of precipitated amorphous wax therefrom.

17. In the production of dewaxed mineral oil, the steps comprising forming a mixture of finely divided solids and a solvent and oil containing crystalline wax and amorphous wax; filtering from the mixture, while the mixture is at a temperature low enough to precipitate crystalline wax and to form in the oil a cloud other than that due to the finely divided solids and sufficiently high to prevent such precipitation of amorphous wax as will impair the filtering of the mixture, said finely divided solids and solids precipitated therein; and then continuously centrifugally removing precipitated wax from a chilled solution of the resulting oil.

' LEO D. JONES. 

